DESCRIPTION (provided by investigator): This proposal builds on two previous studies by the investigator, which found that participation in an established and growing "dual-focus" mutual aid model (Double Trouble in Recovery;DTR) by persons with co-occurring substance use and psychiatric disorders was associated with drug/alcohol abstinence and improved psychiatric outcomes. However, these findings are limited as they are based on studies using an observational design with existing DTR groups and a pre-post design with a historical control. This new application seeks to confirm and significantly extend this research by conducting a randomized clinical trial (RCT) of DTR at multiple treatment sites. The specific study aims are: 1. To conduct a multi-site RCT to determine the efficacy of "dual focus" 12-step mutual aid groups for persons with co-occurring substance use and mental disorders. Substance-using patients who are admitted to six psychiatric outpatient clinics will be randomly assigned within each clinic to (i) DTR group participation plus standard treatment, or (ii) standard treatment as usual. Primary outcomes are drug/alcohol use;psychiatric medication adherence;psychiatric symptoms;quality of life;treatment retention;and re-hospitalization. Major assessments will occur at intake and 6 and 12 months later. 2. To determine the therapeutic mechanisms mediating between DTR participation and behavioral outcomes. Mediating variables will include both "common process" factors across treatments, e.g., coping, self-efficacy and social support;and factors relatively unique to mutual aid, e.g., mutual aid group processes, 12-step attitudes and spirituality. 3. To determine the personal, social/environmental and treatment-related variables that predict DTR affiliation. 4. To describe the development of DTR groups and the conditions needed to sustain them. Federal substance abuse and mental health policy encourages the use of evidence-based interventions, yet rigorous evaluation data are scant for mutual aid groups. In particular, this research will lead to recommendations for improving the integration of formal treatment with mutual aid for persons with co-occurring disorders. Moreover, by conducting the proposed RCT, the study will substantially raise the standard by which mutual aid is evaluated.